This invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device of the active matrix type.
In an active matrix type liquid crystal display device, a group of gate signal lines (scanning signal lines) and a group of drain signal lines (image signal lines) are so formed as to cross one another on the surface of one of a pair of transparent substrates which oppose each other through a liquid crystal layer, on one side of the liquid crystal, and each pixel area encompassed by these signal lines includes a thin film transistor for supplying a drain signal (image signal) through the drain signal line to a pixel electrode when a gate signal (selection signal) is supplied through the gate signal line.
The group of the gate signal lines and the group of the drain signal lines are formed by a microminiaturization process utilizing so-called photolithography. It is therefore customary to inspect whether or not each signal is formed in a disconnected state, or whether or not a short-circuit occurs between the signal lines, during the production process of the liquid crystal display device.
In this case, the inspection is carried out by forming an inspection terminal to which the group of the gate signal lines are connected in common and an inspection terminal to which the group of the drain signal lines are connected in common, on the transparent substrate surface which is to be cut off and separated later, and by bringing an inspection probe into contact with each terminal.
Since the thin film transistor is formed as a MIS transistor by using a part of the area of the group of gate signal lines as its gate electrode and an area where the drain signal lines extend as a drain electrode, measures are taken so as to prevent the signal lines from being concentratedly charged by static electricity and to thus prevent fluctuation of its threshold voltage or its breakdown.
In other words, static electricity is dispersed by forming common wirings for electrostatic protection outside the display area into which the liquid crystal is sealed in and which comprises a group of the pixel areas, and by connecting these common wirings to the gate signal lines and the drain signal lines through electrostatic protection circuits (diodes for electrostatic protection).